The invention relates to a method for controlling brake pressure in a motor vehicle wherein wheel speed signals are used to generate slip signals and wheel acceleration signals, which in turn are used to generate brake pressure control signals.
The quality of the braking retardation of an ABS-controlled vehicle and the pedal reactions depend on the rapidity with which the required optimum pressure level is reached, the amplitude of the pressure modulation having to be very small. The amplitude of the pressure modulation is substantially dependent in this case on the magnitude of the preceding pressure reduction or on how long the period of activation of the discharge valve is.
As an example, a method is known for dimensioning the discharge valve activation time which uses a constant magnitude to correct a value determined from the "prehistory" of the control, and can vary this time as a function of the current wheel behavior.
Also known is a method which uses just such a time value from the prehistory, but calculates it with the aid of a correction value dependent on the wheel acceleration of the previous control cycle, the correction value being inversely proportional to the wheel acceleration.
The disadvantage of these known solutions is that owing to the ever present system delay times the pressure reduction does not match the physical wheel behavior, or that because of roadway defects which are present the ABS control reacts with control fluctuations, for example in the case of small wheel reaccelerations, so that overall the aim of a small pressure modulation is not achieved.